The invention generally pertains to molybdenum, and more specifically, to molybdenum metal and production thereof.
Molybdenum (Mo) is a silvery or platinum colored metallic chemical element that is hard, malleable, ductile, and has a high melting point, among other desirable properties. Thus, molybdenum is commonly used as an additive for metal alloys to impart various properties thereto, and hence to enhance the properties of the metal alloy. For example, molybdenum may be used as a hardening agent, especially for high-temperature applications. However, molybdenum does not naturally occur in pure form. Instead, molybdenum occurs in a combined state. For example, molybdenum ore typically exists as molybdenite (molybdenum disulfide, MOS2). The molybdenum ore may then be processed by roasting it to form molybdic oxide, MoO3.
Molybdic oxide may be directly combined with other metals, such as steel and iron, to form alloys thereof, or molybdic oxide may be further processed to form pure molybdenum. In its pure state, molybdenum metal is tough and ductile and is characterized by moderate hardness, high thermal conductivity, high resistance to corrosion, and a low expansion coefficient. Therefore, molybdenum metal may be used for electrodes in electrically heated glass furnaces, nuclear energy applications, and for casting parts used in missiles, rockets, and aircraft. Molybdenum metal may also be used as a filament material in various electrical applications that are subject to high temperatures, such as X-ray tubes, electronic tubes, and electric furnaces. In addition, molybdenum metal is often used as a catalyst (e.g., in petroleum refining), among other uses or applications.
Processes have been developed for producing molybdenum metal in its pure state. Such a process involves a two-step process. In the first step, a mixture of molybdenum tri-oxide and ammonium di-molybdate is introduced to a first furnace (e.g., a rotary kiln or fluidized bed furnace) to yield molybdenum dioxide, as expressed by the following formula:
2(NH4)MoO4+2MoO3xe2x86x923MoO2+4H2O+N2(g)xe2x80x83xe2x80x83(1)
In the second step, the molybdenum dioxide is transferred to a second furnace (e.g., a pusher furnace) and reacted with hydrogen to form molybdenum powder, for example, as expressed by the following formula:
MoO2+2H2(g)xe2x86x92Mo+2H2Oxe2x80x83xe2x80x83(2)
However, this process for producing molybdenum metal requires multiple batch steps, which is labor intensive, slows production, and increases production costs. In addition, this process requires separate processing equipment (e.g., furnaces) for each step, which increases capital costs and maintenance costs. Furthermore, these processes only produce molybdenum metal having a surface area of about 0.8 square meters per gram (m2/g), or less, and may vary widely in size.
Novel forms of molybdenum metal may be characterized by a surface area of substantially 2.5 m2/g according to BET analysis. Other novel forms of molybdenum metal may be characterized by a substantially uniform size as detected by scanning electron microscopy.
Also disclosed are apparatus and methods for producing molybdenum metal. Apparatus for producing molybdenum metal from a precursor material may comprise a furnace having at least two heating zones, and a process tube extending through the furnace. The precursor material may be introduced into the process tube and moved through each of the at least two heating zones of the furnace. A process gas may be introduced into the process tube, wherein the precursor material reacts with the process gas to form molybdenum metal.
Methods for producing molybdenum metal from a precursor material may comprise the steps of: heating a precursor material to a first temperature in the presence of a reducing gas, and increasing the first temperature at least once to reduce the precursor material and form the molybdenum metal.